FIG. 1 (not drawn to scale) shows an exemplary conventional bifocal contact lens 10 having an optical zone 12. Optical zone 12 is comprised of concentric zones of alternating near viewing regions 14 and distance viewing regions 16. When viewing a distant image through optical zone 12, the image appears focused and clear when viewed through distance regions 16 but out of focus when viewed though near regions 14. A similar effect occurs when viewing a near object. In effect, the wearer experiences an undesirable effect referred to as simultaneous vision in which the image appears in focus but is surrounded by an out-of-focus halo.
Near viewing regions 14 and distance viewing regions 16 are continuous around optical zone 12. Thus, lens 10 may rotate freely in the eye and no ballasting techniques are required to maintain orientation of lens 10. The ability of lens 10 to freely rotate provides for more efficient flushing of the surface of lens 10 with tears when the wearer thereof blinks.
Thus, although conventional bifocal contact lens 10 is efficiently flushed with tears, the wearer may experience undesirable simultaneous vision.
FIG. 2 (not drawn to scale) shows an exemplary conventional translating bifocal contact lens 30 having an optical zone 32. Optical zone 32 is divided into a superior region 34 that is optimized for distance vision and an inferior region 36 that is optimized for near vision. When the wearer looks down to read or view a near object his or her pupil is disposed mostly in the inferior or near-viewing region 36. When the wearer looks forward at a distant object the pupil is mostly disposed in the superior or distance region 34. Thus, translating bifocal contact lens 30 reduces the occurrence of simultaneous vision. The translating bifocal is a popular lens configuration because it enables the wearer to shift the amount of light to the pupil and provides better visual quality than simultaneous bifocal contact lenses.
However, inferior or near region 36 generally has a steeper curve than superior or distance region 34. In order to compensate for that relatively steep curve and maintain a generally round shape, translating bifocal contact lens 30 is typically thicker than other contact lenses and has a large step 38 (i.e., a sudden increase and/or decrease in thickness) between inferior/near region 36 and superior/distance region 34 (which is exaggerated as shown in FIG. 2). The relative thickness of translating bifocal contact lens 30 and the large step 38 between the inferior/near region 36 and superior/distance region 34 thereof may cause discomfort to some wearers.
Furthermore, ballasting techniques (not shown) must be used to orient translating bifocal contact lens 30 such that near objects are viewed through the inferior/near region 36 and distant objects are viewed through the superior/distance region 34. Ballasting techniques reduce the efficiency with which a lens is flushed. The extra thickness of these lenses and the required ballasting techniques reduce the oxygen transfer to the surface of the eye and could lead to an increased risk of corneal edema.
Thus, although reducing simultaneous vision and providing better visual quality than simultaneous bifocal contact lens 10, translating bifocal contact lens 30 reduces oxygen transfer to the eye, is flushed less efficiently, and may be uncomfortable to some wearers.
Therefore, what is needed in the art is a multifocal contact lens that reduces the occurrence of simultaneous vision and which provides improved visual quality without reducing oxygen transfer to the eye.
Furthermore, what is needed in the art is a multifocal contact lens that reduces the occurrence of simultaneous vision and which provides improved visual quality while still providing for relatively efficient flushing of the lens.
Moreover, what is needed in the art is a multifocal contact lens that reduces the occurrence of simultaneous vision and which provides improved visual quality without requiring large steps between visual regions which may cause wearer discomfort.
Lastly, what is needed in the art is a multifocal contact lens that combines the desirable qualities, characteristics, and properties of simultaneous vision contact lenses with those of translating vision contact lenses.